The success of in-casing gravel packs using a slotted liner in a perforated casing is highly dependent on established gravel/formation fine size relationships. With study and experience, it is possible to select the proper gravel size to optimize produtivity while controlling formation fines invasion into the wellbore. Success of the gravel pack is very dependent on effective placement of the gravel. Ordinarily, this can be successfully accomplished in a vertical wellbore.
Most loosely consolidated formations where fines production is likely to occur are located offshore where many wells are drilled from a single platform. Most wells are drilled on an incline, resulting in completions through the pay intervals at an angle. In these wells, it is more difficult to place a gravel pack effectively due to the inclination of the hole. Because of the inclination of inclined or deviated wellbores, conventional gravel packing procedures meet with limited success in these wells.
Gravel packing is a secondary sand placement technique involving the introduction of a fluid suspension of exogenous particulate matter downhole, to fill the wash-out cavities or to "squeeze" to pack into the formation in the vicinity of the well. The term gravel is somewhat loosely applied in the art to encompass hard, rigid particulate matter ranging in size from a coarse sand to pebble size material.
Once the placement of sand and gravel has been accomplished, a slotted liner or "screen" placed as part of the production string helps hold the loose filling material and retard the upstream sand flow through the filler material during production conditions.
Present gravel pack procedures often require a filling of the casing with weighted completion fluid or drilling mud prior to perforating. Thereafter, the production casing is perforated via a casing gun with shots placed in a helical arrangement. Substantial amounts of wellbore fluid are often lost, as in most instances, the wellbore is in an overbalanced condition. If the well is not completely dead following the perforation operation, it is generally "killed" so the perforating tool can be pulled from the borehole. After pulling the perforating tool from the borehole, the production tubing along with a slotted liner is directed into the borehole. As a result of these operations, substantial amounts of expensive workover fluid can be lost during these operations. Because of the density, viscosity and chemical makeup of these workover fluids, damage often occurs to the permeability of a formation. Afterwards, in order to stabilize the sand in the formation, an in-casing gravel pack is generally placed within the wellbore along with additional fluids and chemicals. This results often in additional damage to the permeability of the formation.
Therefore, what is needed is a method for a gravel pack operation in inclined or deviated wells which will minimize permeability damage to the formation caused by workover fluids and chemicals.